This invention relates to a sewing machine specially designed to stitch a zipper to fabrics and more particularly to an apparatus for positioning a zipper in correct position.
When a zipper is to be stitched to the fabric of a skirt, the zipper is first stitched to a fabric lining cloth and then this lining fabric and a front cloth material are sewed together. During this process, the positioning of the lining cloth and the front cloth material is very important since this positioning influences the final grading of stitch work. Therefore, the positioning work requires precision work and several manufacturing steps. To avoid such precision work and manufacturing steps, many kinds of automatic zipper sewing machines have been developed.
FIG. 14 and FIG. 15 illustrate how the conventional zipper sewing machine works when the zipper is being sewed to the skirt. Referring to FIG. 14 and FIG. 15, "a" denotes a sewing machine, "k" denotes a lining cloth with a zipper "l" previously sewed therewith, "j" denotes a front cloth, "j.sub.1 " denotes a sewed portion of the front cloth, and the numeral 30 denotes a casset-set.
At first, the casset-set is placed on a table "m". The lining cloth k with the zipper l previously sewed therewith and the front cloth j are set on the casset-set 30 manually. After clamping the fabric with the casset-set 30, the casset-set is placed on a feeding table "g" of a sewing machine a. An air cylinder "b" is installed on the feed table g and air is supplied to plunger side of the cylinder. The plunger is drawn, and resultantly, a pair of foot presses "i" the casset-set 30 through linkage motion via a shaft "f", a lever "d", and a pressing arm "e". The sewing machine a is then driven by an automatic X-Y coordinate driver (not shown) in direction of X and Y accordingly, and thus the front cloth and the lining cloth k are sewed together.
According to conventional procedures, the front cloth j and the lining cloth k are set manually relying on the human eye. Thus, it is difficult to secure correct positioning and time is wasted in the process. In some cases, the zipper is not symmetrically positioned relative to the center line and therefore the distances p, q (refer to FIG. 16a) are not equal. When the difference is beyond a certain degree, the needle strikes the stopper l.sub.1 of zipper l and the needle is often broken.
Referring to FIG. 16b, if the position of the already sewed portion Sr does not coincide with the position of center line of the zipper, the portion z as shown in FIG. 16b is wrinkled.